The mining industry relies heavily on off-road vehicles to perform a variety of tasks. Specifically, mining trucks are used to haul large amounts of extracted materials throughout a mining site. In the case of underground mining, the trucks are further required to haul the materials throughout tunnels and up various grades to resurface from the extraction site.
The engines of these mining trucks are typically diesel engines capable of producing a large amount of horsepower. Recently, there has been a trend to have the engine power transmitted to truck wheels through an electric drive propulsion system rather than a mechanical drive system. The electric drive propulsion system permits the engine to deliver power more efficiently. It typically consists of a generator or alternator and a wheel motor mounted for delivering torque rim pull to each drive wheel. The electric drive system may also include a throttle sensor that is used to determine an actuation of the throttle which, in turn, may be interpreted by a controller to determine the amount of horsepower or torque rim pull requested by the operator.
Although most manufacturers preclude the release of an engine that does not operate according to specific standards, a slight variation, due to inherent manufacturing constraints, will be allowed. Therefore, a nominal lug curve provided by the manufacturer may not accurately represent the actual operating conditions of similar engines. In addition, once an engine leaves the manufacturer, operating conditions may begin to deviate, possibly further, from those represented by the nominal lug curve. Natural changes, including normal wear of an engine, may contribute to changes in the operating conditions of an engine over time. If control decisions are made based upon nominal lug curve data, inaccuracies in the data can result in operation inefficiencies, which may include unnecessary fuel consumption.
Economic pressures render it is desirable to operate the engine at maximum fuel economy and engine efficiency. This includes operating the engine at the lowest engine speed required to produce the necessary rim pull or horsepower, and avoiding situations that cause the engine to lug. Lugging generally decreases fuel economy by consuming excess fuel without providing the requested rim pull or horsepower.
U.S. Pat. No. 5,939,846 discloses a machine with an electric drive propulsion system and method of determining the maximum horsepower available from the engine at a current operating speed based on an adjustment of the nominal lug curve provided by the manufacturer. Specifically, a regulator continuously adjusts a software variable reflecting an available horsepower limit until an engine reaches a desired operating condition that matches the torque demand. Since this disclosure does not account for deviations from the nominal lug curve, that may occur both when the engine is manufactured and as the engine ages, fuel may be wasted as the regulator continuously corrects the current available horsepower relative to that specified by the nominal lug curve to what the engine can actually deliver.
The present disclosure is directed to one or more of the problems set forth above.